The present invention relates to compositions for polymerizing ethylene, to form an interpolymer product having unique physical properties, to a process for preparing such interpolymers, and to the resulting polymer products. In another aspect, the invention relates to methods of using these polymers in applications requiring unique combinations of physical properties. In still another aspect, the invention relates to the articles prepared from these polymers. The inventive polymers comprise two or more differing regions or segments (blocks) causing the polymer to possess unique physical properties. These multi-block copolymers and polymeric blends comprising the same are usefully employed in the preparation of solid articles such as moldings, films, sheets, and foamed objects by molding, extruding, or other processes, and are useful as components or ingredients in adhesives, laminates, polymeric blends, and other end uses. The resulting products are used in the manufacture of components for automobiles, such as profiles, bumpers and trim parts; packaging materials; electric cable insulation, and other applications.
It has long been known that polymers containing a block-type structure often have superior properties compared to random copolymers and blends. For example, triblock copolymers of styrene and butadiene (SBS) and hydrogenated versions of the same (SEBS) have an excellent combination of heat resistance and elasticity. Other block copolymers are also known in the art. Generally, block copolymers known as thermoplastic elastomers (TPE) have desirable properties due to the presence of “soft” or elastomeric block segments connecting “hard” either crystallizable or glassy blocks in the same polymer. At temperatures up to the melt temperature or glass transition temperature of the hard segments, the polymers demonstrate elastomeric character. At higher temperatures, the polymers become flowable, exhibiting thermoplastic behavior. Known methods of preparing block copolymers include anionic polymerization and controlled free radical polymerization. Unfortunately, these methods of preparing block copolymers require sequential monomer addition and batch processing and the types of monomers that can be usefully employed in such methods are relatively limited. For example, in the anionic polymerization of styrene and butadiene to form a SBS type block copolymer, each polymer chain requires a stoichiometric amount of initiator and the resulting polymers have extremely narrow molecular weight distribution, Mw/Mn, preferably from 1.0 to 1.3. Additionally, anionic and free-radical processes are relatively slow, resulting in poor process economics.
It would be desirable to produce block copolymers catalytically, that is, in a process wherein more than one polymer molecule is produced for each catalyst or initiator molecule. In addition, it would be highly desirable to produce multi-block copolymers having both highly crystalline and amorphous blocks or segments, from a single monomer, ethylene, which is generally unsuited for use in anionic or free-radical polymerizations. Finally, if would be highly desirable to be able to use a continuous process for production of the present multi-block copolymers.
Previous researchers have stated that certain homogeneous coordination polymerization catalysts can be used to prepare polymers having a substantially “block-like” structure by suppressing chain-transfer during the polymerization, for example, by conducting the polymerization process in the absence of a chain transfer agent and at a sufficiently low temperature such that chain transfer by β-hydride elimination or other chain transfer processes is essentially eliminated. Under such conditions, the sequential addition of different monomers was said to result in formation of polymers having sequences or segments of different monomer content. Several examples of such catalyst compositions and processes are reviewed by Coates, Hustad, and Reinartz in Angew. Chem. Int. Ed., 41, 2236-2257 (2002) as well as US-A-2003/0114623.
The use of certain metal alkyl compounds and other compounds, such as hydrogen, as chain transfer agents to interrupt chain growth in olefin polymerizations is well known in the art. In addition, it is known to employ such compounds, especially aluminum alkyl compounds, as scavengers or as cocatalysts in olefin polymerizations. In Macromolecules, 33, 9192-9199 (2000) the use of certain aluminum trialkyl compounds as chain transfer agents in combination with certain paired zirconocene catalyst compositions resulted in polypropylene mixtures containing small quantities of polymer fractions containing both isotactic and atactic chain segments. In Liu and Rytter, Macromolecular Rapid Comm., 22, 952-956 (2001) and Bruaseth and Rytter, Macromolecules, 36, 3026-3034 (2003) mixtures of ethylene and 1-hexene were polymerized by a similar catalyst composition containing trimethylaluminum chain transfer agent.
In U.S. Pat. Nos. 6,380,341 and 6,169,151, use of a “fluxional” metallocene catalyst, that is a metallocene capable of relatively facile conversion between two stereoisomeric forins having differing polymerization characteristics such as differing reactivity ratios was said to result in production of olefin copolymers having a “blocky” structure from propylene.
In JACS. 2004, 126, 10701-10712, Gibson, et al discuss the effects of “catalyzed living polymerization” on molecular weight distribution. The authors define catalyzed living polymerization in this manner:
“. . . if chain transfer to aluminum constitutes the sole transfer mechanism and the exchange of the growing polymer chain between the transition metal and the aluminum centers is very fast and reversible, the polymer chains will appear to be growing on the aluminum centers. This can then reasonably be described as a catalyzed chain growth reaction on aluminum . . . . An attractive manifestation of this type of chain growth reaction is a Poisson distribution of product molecular weights, as opposed to the Schulz-Flory distribution that arises when β-H transfer accompanies propagation.”
The authors reported the results for the catalyzed living homopolymerization of ethylene using an iron containing catalyst in combination with ZnEt2, ZnMe2, or Zn(i-Pr)2. Homoleptic allkyls of aluminum, boron, tin, lithium, magnesium and lead did not induce catalyzed chain growth. Using GaMe3 as cocatalyst resulted in production of a polymer having a narrow molecular weight distribution. However, after analysis of time-dependent product distribution, the authors concluded this reaction was, “not a simple catalyzed chain growth reaction.” The reference fails to disclose the use of two or more catalysts in combination with a chain shuttling agent to make multi-block copolymers. Similar processes employing single catalysts have been described in U.S. Pat. Nos. 5,210,338, 5,276,220, and 6,444,867.
Earlier workers have claimed to have formed block copolymers using a single Ziegler-Natta type catalyst in multiple reactors arranged in series, see for example U.S. Pat. Nos. 3,970,719 and 4,039,632. Additional Ziegler-Natta based processes and polymers are disclosed in U.S. Pat. Nos. 4,971,936; 5,089,573; 5,118,767; 5,118,768; 5,134,209; 5,229,477; 5,270,276; 5,270,410; 5,294,581; 5,543,458; 5,550,194; and 5,693,713, as well as in EP-A-470,171 and EP-A-500,530.
It is known that random defects occur in polymers prepared from single monomers using, for example, Ni and Pd-diimine catalysts. The catalyst engages in “chain walking” during polymerization forming branched chains, highly branched (hyper-branched), or even dendermeric branched chains in the resulting polymer. Examples of this type of polymerization are found in Chem. Rev., 100, 1169-1203 (2000), Macromolecular Chemistry and Physics, 205, 897-906, (2004), and elsewhere. It is also known that long chain branched polymer units may be prepared from ethylene using certain homogeneous polymerization catalysts such as 1-, and 2-t-butyldimethylsiloxy substituted bis(indenyl)zirconium complexes with metlhylalumoxane cocatalyst. Examples of this type of polymerization are found in J. Mol. Catal. A: Chemical, 102 59-65 (1995); Macromolecules 21, 617-622 (1988); J. Mol. Catal. A: Chemical, 185, 57-64 (2002), and J. Am. Chem. Soc., 117, 6414-6415 (1995).
Despite the advances by the foregoing researchers, there remains a need in the art for a polymerization process that is capable of preparing block like copolymers, especially multi-block copolymers, and most especially linear multi-block copolymers, in high yield and selectivity from a single monomer, ethylene, by the use of a shuttling agent. In addition it would be desirable to provide such an improved process that is capable of preparing multi-block copolymers, especially linear multi-block copolymers, having a relatively narrow molecular weight distribution. It would further be desirable to provide an improved process for preparing copolymers having more than two segments or blocks. Furthermore, it would be desirable to provide a process for identifying combinations of catalysts and chain shuttling agents capable of making such multi-block copolymers. Even further, it would be desirable to provide a process for independent control of the order of the various polymer blocks, especially a process for preparing olefin block copolymers containing terminal blocks having high crystallinity and/or functionality from a single olefin reagent. Finally, it would be desirable to provide an improved process for preparing any of the foregoing desirable polymer products in a continuous process, without required sequential addition of two of more monomers. Highly desirably, such process allows for independent control of the quantity and/or identity of the shuttling agent(s) and/or catalysts used.